SOI semiconductor integrated circuit for eliminating floating body effects in SOI MOSFETs and method of fabricating the same

ABSTRACT

A silicon-on-insulator (SOI) integrated circuit and a method of fabricating the SOI integrated circuit are provided. At least one isolated transistor active region and a body line are formed on an SOI substrate. The transistor active region and the body line are surrounded by an isolation layer which is in contact with a buried insulating layer of the SOI substrate. A portion of the sidewall of the transistor active region is extended to the body line. Thus, the transistor active region is electrically connected to the body line through a body extension. The body extension is covered with a body insulating layer. An insulated gate pattern is formed over the transistor active region, and one end of the gate pattern is overlapped with the body insulating layer.

RELATED APPLICATION

This application is a divisional of copending U.S. application Ser. No.09/695,341, filed on Oct. 24, 2000, now U.S. Pat. No. 6,498,370, whichclaims the benefit of Provisional application Ser. No. 60/161,479, filedOct. 25, 1999 the contents of which are incorporated herein in theirentirety by reference.

FIELD OF THE INVENTION

The present invention generally relates to silicon-on-insulator (SOI)technology, and more particularly to an SOI semiconductor integratedcircuit for eliminating floating body effects in SOI MOSFETs and amethod of fabricating the same.

DESCRIPTION OF THE RELATED ART

In the semiconductor manufacturing industry, there has been a great dealof attention paid to reducing parasitic capacitance and resistance toincrease the operating speed of semiconductor integrated circuits. SOIMOSFETs have been demonstrated to be superior to bulk silicon MOSFETs interms of low power, high speed very large scale integration (VLSI)applications because of their inherent merits such as less junctioncapacitance and better device isolation. In addition, there are manyadvantages in SOI devices such as better immunity to soft errors,reduction in dynamic power, improvement in latch-up resistance even withincreased packing density. Despite the above outstanding features of SOIdevices, SOI integrated circuits have suffered some lack of commercialsuccess due to technical problems in material processing and devicedesign.

FIG. 1 depicts a typical structure of an SOI MOSFET according to theprior art. The SOI MOSFET includes a gate electrode 20, a gatedielectric 21, a source 23 and drain 24 on insulating layer 15. Abackside surface of the insulating layer 15 is in contact with asupporting substrate 10.

Since the body region 30 of the SOI MOSFET is isolated by the insulatinglayer 15, it is electrically isolated and therefore its voltage varieswith the voltage applied to either source region 23, drain region 24, orgate electrode 20.

The voltage fluctuation of the body region 30 in SOI MOSFET, commonlyreferred to as the floating body effect (FBE), causes detrimentaleffects for the proper operation of SOT devices. The most common ofthese detrimental effects are the kink effect and the bipolar effect.With the channel region of the device partially depleted and a highdrain voltage applied, the electric field created in the device causesimpact ionization near the drain region 24.

Accordingly, in the event that the SOI MOSFET is an SOI N-MOSFET, thegenerated holes are injected into the body thereby creating a positivelycharged body. The first consequence of this positive charge accumulatedin the body 30 is the increase of the body potential resulting in adecrease of the threshold voltage (V_(T)) of the SOI MOSFET. Since thedecrease of the threshold voltage raises the drain current, thevariation of threshold voltage shows up as kinks in the outputcharacteristics of the SOI MOSFETs.

Another consequence of the voltage increase is the eventual turn-on ofthe lateral bipolar structure since the MOSFET includes a lateralbipolar transistor, i.e., the n-p-n construction 23, 30, and 24. As thebody 30 of the MOSFET becomes positively biased, the source-body (23-30)junction, corresponding to emitter-base junction of the lateral n-p-nconstruction, becomes forward biased, and electrons are injected fromthe source 23 into the body region 30. The injected electrons reachingthe drain depletion region add to the drain current. Consequently, thedrain current is dominantly controlled by the parasitic bipolartransistor rather than by the channel current under the gate electrodecontrol. This effect is referred to as the parasitic “bipolar” effect.The parasitic bipolar action of the SOI MOSFET induces a “dynamicleakage current” (DLC) especially in a switching circuit.

In a MUX (multiplexer) circuit as depicted in FIG. 2A, if the appliedvoltages at nodes A and B are high, then the output node C will be high.If the gate voltage of the node A is switched to a low voltage, then theoutput node C should be kept to a high voltage. However, in a state thatthe nodes A and C keep a low voltage and a high voltage, respectively,if the voltage at node B is switched to a low voltage for some reason,the output voltage at node C drops instantaneously by the dynamicleakage mechanism due to the parasitic bipolar effect. FIG. 2Billustrates the instantaneous drop of the output voltage at node C inthe multiplexer circuit according to the prior art. Here, the x-axisrepresents time (t) and the y-axis represents voltage of the node C.

In order to remedy those detrimental effects due to the floating bodyeffect observed in SOI MOSFETs, several technical approaches have beenproposed. For instance, F. Assaderaghi et al. proposed a technique forreducing the floating body effect in their technical paper entitled, “Adynamic threshold voltage MOSFET (DTMOS) for very low voltageoperation,” published in IEEE Electron Device Lett., pp.510-512, Vol.15,No.12, 1994. F. Assaderaghi et al. tried to eliminate the floating bodyeffect by tying the floating body to the gate of the SOI MOSFET.However, since the dynamic leakage current cannot be avoided betweensource and drain when the gate voltage is high while keeping source anddrain low, they pointed out that their approach is only applicable tothe low voltage operation.

As another approach to resolve the floating body problem in SOI devices,J. W. Sleight et al. proposed a Schottky body contact technology in atechnical paper entitled, “DC and transient characterization of acompact Schottky body contact technology for SOI transistors,” publishedin IEEE Transactions on Electron Devices, pp.1451-1456, Vol.46, No.7,July 1999. This technical paper provides a self-aligned Schottky diodemethod for body contacting partially depleted SOI transistors. In theirpaper, Schottky diodes are placed at source/drain terminals, allowingthe floating body to be tied to the source/drain region.

FIGS. 3A and 3B are schematic layout diagrams for implementing bodycontact tied to source/drain and gate, respectively, according to theprior art. Referring to FIG. 3A, n⁺ source 23 is tied to the body 30through p⁺ regions 31. Referring to FIG. 3B illustrating the gate-bodycontact in accordance with the first prior art paper mentioned above,the body 30 is electrically connected to the gate electrode 20 throughelectrical contact 33.

However, it should be noted that the body contacting schemes either tosource or gate disclosed in the prior art have fundamental limitationsin their application to commercial SOI integrated circuits. Namely,since only the weak parts vulnerable to the dynamic leakage current outof the whole circuit are manually cured by contacting the floating bodyaccording to the prior art it is difficult to resolve the inherentfloating body problem in SOI integrated circuits.

For instance, only 50 to 100 thousand transistors are usuallybody-contacted to remedy the floating body effect out of 1.5 milliontransistors comprising the 64-bit microprocessor fabricated on SOIsubstrate.

SUMMARY OF THE INVENTION

In view of these problems, there is need for a method and structure forfundamentally eliminating the floating body effect in SOI semiconductorintegrated circuits, which is not subject to these limitations.

Accordingly, it is an object of the present invention to provide atechnique to eliminate the floating body effect in SOI integratedcircuits. It is another object of the present invention to provide atechnique to resolve the kink effect in SOI integrated circuits.

It is another object of the present invention to provide a technique toeliminate the parasitic bipolar effect and consequently the dynamicleakage current in SOI integrated circuits.

It is another object of the present invention to provide a technique toeliminate the floating body effect, which is applicable to commercialSOI products.

It is another object of the present invention to provide a completesolution to eliminate the floating body effect while keeping theconventional layout compatibility.

Accordingly, the invention is directed to a SOI semiconductor integratedcircuit and a method of making the same. The SOI integrated circuit ofthe invention is formed on an SOI substrate including a supportingsubstrate, a buried insulating layer on the supporting substrate and asemiconductor layer of a first conductivity type on the buriedinsulating layer. The SOI integrated circuit of the invention includesat least one isolated transistor active region including a predeterminedregion of the semiconductor layer. A body line of the first conductivitytype is disposed at one side of the transistor active region, the bodyline including a portion of the semiconductor layer. An isolation layersurrounds sidewalls of the transistor active region and the body line,the isolation layer being in contact with the buried insulating layer. Abody extension of the first conductivity type extends from apredetermined sidewall of the transistor active region and is connectedto the body line, the body extension being thinner than the transistoractive region. A body insulating layer is formed on the body extension.An insulated gate pattern crosses over the transistor active region, theinsulated gate pattern overlapping with the body insulating layer.

In accordance with the present invention, provided are SOI semiconductorintegrated circuits having a body extension which connects a body regionof an SOI MOSFET to a body line tied to the power line or the groundline and methods of fabricating the SOI semiconductor integratedcircuits.

An SOI integrated circuit according to an embodiment of the presentinvention comprises at least one isolated SOI MOSFET surrounded byinsulator, a body line disposed at one side of the SOI MOSFET and a bodyextension which electrically connects a sidewall of a body region of theSOI MOSFET to the body line. Therefore, a plurality of SOI MOSFETs maybe disposed at one side of the body line. In addition, the plurality ofSOI MOSFETs may be disposed at both sides of the body line.

In one embodiment, the first conductivity type is P type. In analternative embodiment, the first conductivity type is N type. In oneembodiment, the SOI integrated circuit includes a metal silicide layerformed on the body line.

In one embodiment, a gate insulating layer is interposed between theinsulated gate pattern and the transistor active region and one end ofthe insulated gate pattern is overlapped with the body insulating layer.The body insulating layer is thicker than the gate insulating layer.Thus, it can prevent an inversion channel from being formed at the bodyextension regardless of the voltage applied to the insulated gatepattern. As a result, it becomes possible to implement an improved SOIMOSFET without floating bodies in the whole SOI integrated circuits.

The invention is also directed to a method of making a SOI semiconductorintegrated circuit on an SOI substrate including a supporting substrate,a buried insulating layer on the supporting substrate and asemiconductor layer of a first conductivity type on the buriedinsulating layer. In accordance with the method, a predetermined regionof the semiconductor layer is etched to form a trench region defining atleast one isolated transistor active region and a body line activeregion at one side of the transistor active region and concurrentlyleaving a semiconductor residue layer, which is thinner than thesemiconductor layer at a bottom of the trench region. The semiconductorresidue layer is selectively etched until the buried insulating layer isexposed, thereby forming an isolation region and concurrently leaving abody extension of the first conductivity type connecting the transistoractive region to th4 body line active region. A body insulating layerand an isolation layer are formed on the body extension and the exposedburied insulating layer, respectively. An insulated gate pattern isformed crossing over the transistor active region and overlapping withthe body insulating layer. The body line active region is doped withimpurities of the first conductivity type to form a body line.

A method of fabricating the SOI integrated circuit in accordance withthe invention includes forming at least one SOI MOSFET at an SOIsubstrate, forming a body line disposed at one side of the SOI MOSFETand forming a body extension that electrically connects a body region ofthe SOI MOSFET to the body line. Here, the SOI substrate includes asupporting substrate, a buried insulating layer formed on the supportingsubstrate and a semiconductor layer formed on the buried insulatinglayer. Thus, a plurality of SOI MOSFETs may be formed at one side of thebody line or at both sides of the bit line.

The method of forming the SOI MOSFET, the body line and the bodyextension comprises etching a predetermined region of the semiconductorlayer to form a trench region defining at least one isolated transistoractive region and a body line active region at one side of thetransistor active region. The depth of the trench region is smaller thanthe thickness of the semiconductor layer. Thus, a semiconductor residuelayer, which is thinner than the semiconductor layer, exists at thebottom of the trench region. A predetermined region of the semiconductorresidue layer is then selectively etched until the buried insulatinglayer is exposed, thereby leaving a body extension that connects thetransistor active region to the body line. Accordingly, an isolationregion exposing the buried insulating layer is formed. As a result, theisolation region is deeper than the trench region exposing the bodyextension.

Subsequently, a body insulating layer and an isolation layer are formedin the trench region exposing the body extension and in the isolationregion exposing the buried insulating layer, respectively. An insulatedgate pattern crossing over the transistor active region is formed. Thegate pattern is formed so that one end of the gate pattern is overlappedwith the body insulating layer. Here, a gate insulating layer is formedbetween the gate pattern and the transistor active region. The bodyinsulating layer is thicker than the gate insulating layer. Thus, eventhough a predetermined voltage in the range of operating voltage isapplied to the gate pattern, it can prevent an inversion channel frombeing formed at the body extension under the body insulating layer.Impurity ions having the same conductivity type as the semiconductorlayer, i.e., a body region of the SOI MOSFET are implanted into the bodyline active region to form a body line having a low resistivity.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a schematic cross-sectional view illustrating a typical SOIMOSFET in accordance with the prior art.

FIG. 2A is a schematic diagram illustrating a prior art multiplexercircuit.

FIG. 2B is a plot illustrating the dynamic leakage current occurring dueto the floating body effect in the prior art circuit of FIG. 2A.

FIGS. 3A and 3B are schematic layouts for body contacted SOI MOSFETs inaccordance with the prior art.

FIG. 4A is a top view of one embodiment of an SOI integrated circuit inaccordance with the present invention.

FIG. 4B is a top view of another embodiment of an SOI integrated circuitin accordance with the present invention.

FIG. 5 is a schematic perspective view of the SOI integrated circuit inaccordance with the present invention.

FIGS. 6A, 7A, 8A, 9A, 10A and 11A are cross-sectional views taken alongthe line I—I′ of FIG. 4A for illustrating a method of fabricating SOIintegrated circuit according to one embodiment of the present invention.

FIGS. 6B, 7B, 8B, 9B, 10B and 11B are cross-sectional views taken alongthe line II—II′ of FIG. 4A for illustrating a method of fabricating SOIintegrated circuit according to one embodiment of the present invention.

FIGS. 6C, 7C, 8C, 9C, 10C and 11C are cross-sectional views taken alongthe line III—III′ of FIG. 4A for illustrating a method of fabricatingSOT integrated circuit according to one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The present invention will be explained in detail with reference to theaccompanying drawings. FIGS. 4A and 5 are a top view and a perspectiveview, respectively, showing a portion of an SOI integrated circuitaccording to an embodiment of the present invention. An SOI integratedcircuit in accordance with the invention including N-MOSFETs will bedescribed with reference to FIGS. 4A and 5. However, the presentinvention is applicable to SOI integrated circuits including P-MOSFETs.Also, the SOI integrated circuit of the present invention could beimplemented using N-MOSFETs and P-MOSFETs.

Referring to FIGS. 4A and 5, at least one isolated transistor activeregion 1 a is located at a predetermined region of an SOI substrate. Abody line 1 b is disposed at one side of the transistor active region 1a. In detail, the transistor active region 1 a may be disposed at oneside of the body line 1 b. The body line 1 b is electrically connectedto a body extension 1 e which is extended from a sidewall of thetransistor active region 1 a. Also, the body line 1 b preferably has astraight line shape. The SOI substrate includes a supporting substrate53, a buried insulating layer 51 stacked on the supporting substrate 53,and a semiconductor layer stacked on the buried insulating layer 51. Thesemiconductor layer has a first conductivity type. The firstconductivity type may be a P-type or an N-type. In the event that thesemiconductor layer is a P-type, an SOI N-MOSFET is formed at thesemiconductor layer. In the event that the semiconductor layer is anN-type, an SOI P-MOSFET is formed at the semiconductor layer. Thesemiconductor layer may be a silicon layer, a germanium layer or acompound semiconductor layer.

The transistor active region 1 a, the body line 1 b and the bodyextension 1 e are formed of portions of the semiconductor layer. Also,these three regions have the same conductivity type. The body extension1 e is thinner than the transistor active region 1 a and the body line 1b, and the bottom surface of the body extension 1 e is in contact withthe buried insulating layer 51. Thus, the top surface of the bodyextension 1 e is lower than those of the transistor active region 1 aand the body line 1 b. The top surface of the body extension 1 e iscovered with a body insulating layer 3 a. Also, the buried insulatinglayer 51 at the periphery of the transistor active region 1 a, the bodyline 1 b and the body extension 1 e is covered with an isolation layer(not shown).

An insulated gate pattern including a gate electrode 5 is stacked overthe transistor active region 1 a. The gate electrode 5 crosses over thetransistor active region 1 a, and one end of the gate electrode 5 isoverlapped with the body insulating layer 3 a. A gate insulating layer(not shown) is interposed between the gate electrode 5 and thetransistor active region 1 a. The gate insulating layer is thinner thanthe body insulating layer 3 a. Thus, even though an operating voltage isapplied to the gate electrode 5, it can prevent an inversion channelfrom being formed at the body extension 1 e under the body insulatinglayer 3 a.

A source region 1 s of a second conductivity type is formed at thetransistor region 1 a which is located at one side of the gate electrode5, and a drain region 1 d of the second conductivity type is formed atthe transistor region 1 a which is located at the other side of the gateelectrode 5. Accordingly, the transistor active region 1 a under thegate electrode 5 corresponds to a body region 1 c including a channelregion. The gate electrode 5, the source/drain regions 1 s and 1 d, andthe body region 1 c constitute an SOI MOSFET. In addition, an insulatingspacer (not shown) may be formed on a sidewall of the gate electrode 5or the gate pattern including the gate electrode 5. A metal silicidelayer (not shown) may be selectively stacked on the source/drain regions1 s and 1 d and the body line 1 b. The metal silicide layer iselectrically isolated from the gate electrode 5 due to the presence ofthe insulating spacer. Also, the metal silicide layer may be furtherstacked on the gate electrode 5.

The SOI substrate including the SOI MOSFET and the metal silicide layeris covered with an interlayer insulating layer (not shown). Aninterconnection line 9 such as a power line or a ground line is disposedon the interlayer insulating layer. The interconnection line 9 iselectrically connected to the body line 1 b through a contact hole 7penetrating a portion of the interlayer insulating layer. Here, in theevent that the SOI MOSFET is a P-MOSFET, the interconnection linecorresponds to the power line. In the event that the SOI MOSFET is anN-MOSFET, the interconnection line corresponds to the ground line.

A plurality of SOI MOSFETs may be disposed at both sides of the bodyline 1 b, as shown in FIG. 4B. Here, each of the SOI MOSFETs has thesame structure as the SOI MOSFET described in connection with FIGS. 4Aand 5.

FIGS. 6A to 11A, FIGS. 6B to 11B and FIGS. 6C to 11C are cross-sectionalviews for illustrating fabrication methods of SOI integrated circuitsaccording to the present invention. FIGS. 6A to 11A are cross-sectionalviews taken along the line I—I′ of FIG. 4A, and FIGS. 6B to 11B arecross-sectional views taken along the line II—II′ of FIG. 4. Also, FIGS.6C to 11C are cross-sectional views taken along the line III—III′ ofFIG. 4.

Referring to FIGS. 6A, 6B and 6C, a trench mask layer 60 is formed on anSOI substrate 2. The SOI substrate 2 includes a supporting substrate 53,a buried insulating layer 51 formed on the supporting substrate 53 and asemiconductor layer 1 formed on the buried insulating layer 51. Here,the semiconductor layer 1 has a first conductivity type such as aP-type. However, the first conductivity type may be an N-type. Thus, thetrench mask layer 60 is formed on the semiconductor layer 1 of the firstconductivity type. The trench mask layer 60 comprises a pad oxide layer55 and a pad nitride layer 57 which are sequentially stacked. Inaddition, the trench mask layer may further comprise a hard mask layer59 formed on the pad nitride layer 57. The hard mask layer 59 ispreferably formed of a CVD oxide layer having a high etching selectivitywith respect to the semiconductor layer 1 such as a silicon layer. Firstphotoresist patterns 61 are formed on the trench mask layer 60. At leastone of the first photoresist patterns 61 defines at least one isolatedtransistor active region. The other defines a body line active region atone side of the transistor active region.

Referring to FIGS. 7A, 7B and 7C, the trench mask layer 60 is etchedusing the first photoresist patterns 61 as etching masks until thesemiconductor layer 1 is exposed. As a result, at least one first trenchmask pattern 60 a and a second trench mask pattern 60 b are formed. Thefirst trench mask pattern 60 a comprises a first pad oxide pattern 55 a,a first pad nitride pattern 57 a and a first hard mask pattern 59 awhich are sequentially stacked. Similarly, the second trench maskpattern 60 b comprises a second pad oxide pattern 55 b, a second padnitride pattern 57 b and a second hard mask pattern 59 b which aresequentially stacked. The first photoresist patterns 61 are thenremoved.

Subsequently, the exposed semiconductor layer 1 is etched using thefirst and second trench mask patterns 60 a and 60 b as etching masks, tothereby form a trench region T1. At this time, the exposed semiconductorlayer 1 is etched by a predetermined thickness which is thinner thanthat of the semiconductor layer 1. As a result, a semiconductor residuelayer exists at the bottom of the trench region T1. Also, at least onetransistor active region 1 a and a body line active region 1 b aredefined by the trench region T1. Accordingly, the buried insulatinglayer 51 outside the transistor active region 1 a and the body lineactive region 1 b is still covered with the semiconductor residue layer.

Referring to FIGS. 8A, 8B and 8C, a second photoresist pattern 63 isformed on a predetermined region of the semiconductor residue layer. Thesecond photoresist pattern 63 covers a portion of the semiconductorresidue layer between the transistor active region 1 a and the body lineactive region 1 b, as shown in FIGS. 8A and 8C. The semiconductorresidue layer is etched using the second photoresist pattern 63 and thefirst and second trench mask patterns 60 a and 60 b as etching masksuntil the buried insulating layer 51 is exposed. As a result, anisolation region T2 exposing the buried insulating layer 51 is formed.At this time, a body extension 1 e including a portion of thesemiconductor residue layer is also formed under the second photoresistpattern 63, as shown in FIGS. 8A and 8C. Therefore, the body line activeregion 1 b is electrically connected to the transistor active region 1 athrough the body extension 1 e.

Referring to FIGS. 9A, 9B and 9C, the second photoresist pattern 63 isthen removed. An insulating layer such as a CVD oxide layer is formed onthe entire surface of the substrate including the trench region T1 andthe isolation region T2. At this time, it is preferable that the trenchregion T1 and the isolation region T2 be completely filled with theinsulating layer.

The insulating layer is then planarized until the first and secondtrench mask patterns 60 a and 60 b are exposed, thereby forming a bodyinsulating layer 3 a on the body extension 1 e as well as an isolationlayer 3 b on the buried insulating layer 51. At this time, the first andsecond pad nitride patterns 57 a and 57 b act as etch stoppers. Thus, inthe event that the trench mask layer 60 comprises the CVD oxide layer59, the first and second hard mask patterns 59 a and 59 b are removedduring the planarization process such as an etch-back process or a CMP(chemical mechanical polishing) process. As a result, first and secondtransformed trench mask patterns 60 a and 60 b are left after formationof the body insulating layer 3 a and the isolation layer 3 b.

Referring to FIGS. 10A, 10B and 10C, the first and second transformedtrench mask patterns 60 a and 60 b are then removed using a conventionaltechnique, to thereby expose the transistor active region 1 a and thebody line active region 1 b. A gate insulating layer 65 is formed on theexposed transistor active region 1 a and the exposed body line activeregion 1 b. A gate material layer is formed on the entire surface of thesubstrate including the gate insulating layer 65. The gate materiallayer is formed by sequentially stacking a conductive layer and acapping insulating layer. Preferably, the conductive layer is formed ofa doped polysilicon layer and the capping insulating layer is formed ofa CVD oxide layer or a silicon nitride layer. Alternatively, the gatematerial layer may be formed of only the conductive layer. The gatematerial layer is then patterned to form an insulated gate pattern 67crossing over the transistor active region 1 a. Also, one end of thegate pattern 67 is overlapped with the body insulating layer 3 a, asshown in FIGS. 10A and 10C. In the event that the gate material layer isformed by sequentially stacking the conductive layer and the cappinginsulating layer, the insulated gate pattern 67 comprises a gateelectrode 5 formed of the conductive layer and a capping insulatinglayer pattern 6 formed of the capping insulating layer. However, in theevent that the formation of the capping insulating layer is omitted, theinsulated gate pattern 67 is formed of only the gate electrode 5.

Impurities of a second conductivity type are selectively implanted intothe transistor active region 1 a using the gate pattern 67 as animplantation mask, thereby forming low concentration impurity regions 1s and 1 d at both sides of the gate pattern 67, respectively. The secondconductivity type is opposite to the first conductivity type. Forexample, if the first conductivity type is P-type, the secondconductivity type is N-type. The transistor active region 1 a betweenthe low concentration impurity regions 1 s and 1 d corresponds to a bodyregion 1 c.

The body region 1 c includes a channel region which is located under thegate pattern 67. Referring to FIGS. 11A, 11B and 11C, an insulatingspacer 69 is then formed on the sidewall of the insulated gate pattern67 using a conventional technique. The insulating spacer 69 is formed ofa silicon oxide layer or a silicon nitride layer. Subsequently,impurities of the second conductivity type are selectively implantedinto the transistor active region 1 a using the gate pattern 67 and theinsulating spacer 69 as implantation masks, thereby forming highconcentration impurity regions 1 s and 1 d at both sides of the gatepattern 67. As a result, the low concentration impurity regions 1 s and1 d exist under the insulating spacer 69. Thus, LDD(lightly dopeddrain)-type source and drain regions 1 s and 1 d are formed at bothsides of the gate pattern 67. Therefore, the body region 1 c iselectrically connected to the body line active region 1 b through thebody extension 1 e, as shown in FIGS. 11A, 11B and 11C. Here, the gateelectrode 5, the source/drain regions 1 s and 1 d, and the body region 1c constitute an SOI MOSFET.

Impurities of the first conductivity type are selectively implanted intothe body line active region 1 b in order to form a body line 1 b havinga relatively low resistance. A cleaning process is applied to thesurface of the resultant structure, thereby exposing the surfaces of thesource and drain regions 1 s and 1 d and the body line 1 b. A metalsuicide layer 71 may be selectively formed on the exposed body line 1 bas well as the exposed source and drain regions 1 s and 1 d using aconventional SALICIDE(self-aligned suicide) process. The metal silicidelayer 71 is formed of a refractory metal suicide layer such as atitanium silicide layer, a tantalum silicide layer, or a cobalt silicidelayer. In the event that the gate pattern 67 is formed of only the gateelectrode 5, the metal suicide layer 71 is also formed on the gateelectrode 5.

An interlayer insulating layer (not shown) is formed on the entiresurface of the substrate including the metal suicide layer 71. Theinterlayer insulating layer is patterned to form a contact hole 7 (seeFIG. 4) exposing a portion of the body line 1 b. A conductive layerfilling the contact hole 7 is formed on the interlayer insulating layerand patterned to form a interconnection line 9 (see FIGS. 4 and 5) whichis electrically connected to the body line 1 b via the contact hole 7.The interconnection line 9 may be a power line or a ground line. Forexample, if the SOI MOSFET is an N-MOSFET, the interconnection line 9corresponds to the ground line. If the SOI MOSFET is a P-MOSFET, theinterconnection line 9 corresponds to the power line.

As described above, the present invention can prevent the body region ofthe SOI MOSFET from being electrically floated. Therefore, it can beused to realize reliable and compact SOI integrated circuits.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the following claims.

What is claimed is:
 1. A method of fabricating a silicon-on-insulator(SOI) semiconductor integrated circuit on an SOI substrate including asupporting substrate, a buried insulating layer on the supportingsubstrate and a semiconductor layer of a first conductivity type on theburied insulating layer, the method comprising: etching a predeterminedregion of the semiconductor layer, thereby forming a trench regiondefining at least one isolated transistor active region and a body lineactive region at one side of the transistor active region andconcurrently leaving a semiconductor residue layer, which is thinnerthan the semiconductor layer, at a bottom of the trench region;selectively etching the semiconductor residue layer until the buriedinsulating layer is exposed, thereby forming an isolation region andconcurrently leaving a body extension of the first conductivity typeconnecting the transistor active region to the body line active region;forming a body insulating layer and an isolation layer on the bodyextension and the exposed buried insulating layer, respectively; formingan insulated gate pattern crossing over the transistor active region andoverlapping with the body insulating layer; and doping the body lineactive region with impurities of the first conductivity type to form abody line.
 2. The method of claim 1, wherein forming the trench regionand the semiconductor residue layer comprises: forming at least onefirst trench mask pattern and a second trench mask pattern on thesemiconductor layer; and etching the semiconductor layer by apredetermined thickness which is thinner than the semiconductor layerusing the first and second trench mask patterns as etching masks.
 3. Themethod of claim 2, wherein forming the first and second trench maskpatterns comprises: forming a trench mask layer on the semiconductorlayer; and patterning the trench mask layer.
 4. The method of claim 3,wherein the trench mask layer is formed by sequentially stacking a padoxide layer and a pad nitride layer on the semiconductor layer.
 5. Themethod of claim 3, wherein the trench mask layer is formed bysequentially stacking a pad oxide layer, a pad nitride layer and a hardmask layer on the semiconductor layer.
 6. The method of claim 2, whereinforming the body insulating layer and the isolation layer comprises:forming an insulating layer filling the trench region and the isolationregion on an entire surface of the resultant structure having theisolation region; planarizing the insulating layer until the first andsecond trench mask patterns are exposed; and removing the first andsecond trench mask patterns to expose the transistor active region andthe body line active region.
 7. The method of claim 1, wherein formingthe insulated gate pattern comprises: forming a gate insulating layer onthe transistor active region and the body line active region; forming agate material layer on an entire surface of the resultant structurehaving the gate insulating layer; and patterning the gate materiallayer.
 8. The method of claim 7, wherein the gate material layer isformed of a conductive layer.
 9. The method of claim 7, wherein the gatematerial layer is formed by sequentially stacking a conductive layer anda capping insulating layer.
 10. The method of claim 1, furthercomprising forming an insulating spacer on the sidewall of the insulatedgate pattern.
 11. The method of claim 10, further comprising selectivelyforming a metal silicide layer on the body line and the transistoractive region at both sides of the gate pattern.
 12. The method of claim12, wherein the metal silicide layer is formed using a salicide(self-aligned silicide) process.
 13. The method of claim 1, furthercomprising forming a source region at the transistor active region whichis located at one side of the gate pattern and a drain region at thetransistor active region which is located at the other side of the gatepattern, the source and drain regions being doped with impurities of asecond conductivity type opposite to the first conductivity type. 14.The method of claim 1, further comprising: forming an interlayerinsulating layer on an entire surface of the resultant structure havingthe gate pattern and the body line; patterning the interlayer insulatinglayer to form a contact hole exposing a portion of the body line; andforming one of a power line and a ground line on the interlayerinsulating layer, the one of the power line and the ground line beingelectrically connected to the body line through the contact hole.